Plastics sabot



y 9, 1961 s. P. PROSEN ET AL 2,983,224

PLASTICS SABOT Filed Jan. 30, 1958 2 Sheets-Sheet 1 FIG.1.

INVENTORS STANLEY P. PROSEN BY FREDRICK RBARNET ATTYS.

May 9, 1961 s. P. PROSEN ET AL 2,983,224

PLASTICS SABOT Filed Jan. so, 1958 a 2 Sheets-Sheet 2 34 27 I FICA.

INVENTORS STANLEY P. PROSEN FRE RICK R. BARNET BY ATTYS.

Unite PLASTICS SABOT Stanley P. Prosen, Lanham, and Fredrick R. Barnet,Kensington, Md., assignors to the United States of America asrepresented by the Secretary of the Navy Filed Jan. so, 1958, set. No.712,283

11 Claims. (Cl. 102-52) (Granted under Title 35, US. Code (1952), see.266) efieotive against high flying aircraft and against the thick armourplate of present day tanks and ships.

In order to achieve this high velocity, it has been the practice toadapt sub-caliber projectiles so that they can be fired from a highercaliber gun. This in effect, provides a greaterrthan normal amount ofpropellant powder for propelling the projectile. The sub-caliberprojectile, not being as heavy as the standard projectile, therefore,has a much greater amount of energy imparted to it and thus attains agreater velocity. One method of adapting a projectile for firing from ahigher caliber gun is to encase the projectile in an expendable sabotwhich provides a' gas seal as the projectile moves through the bore ofthe gun and which disintegrates as it emerges therefrom so that it doesnot unduly interfere with the trajectory of the projectile. I

Plastics or fiber reinforced plastics possess certain des-irableproperties which make them suitable foruse as a sabot material, sincethey are light weight non-critical materials and are easily fabricated.l

In spite of the desirable properties of plastics, plastics materialshave certain disadvantages for use as sabot material, the majordisadvantage being that those plastics-which possessrthe requiredstrength do not engrave properly as the projectile moves through the.bore of the gun while plastics which engrave properly have insufiicientstrength to withstand the initial pressure build-up in the' chamber asthe gun is fired. w Most sabots are manufactured by machining a plasticsbillet into a cup-shape of suitable interior dimensions to provide atapered interference fit between the projectile and the sabot and ofexternal dimensions compatiblewith the bore'of the gun. The machiningprocess is expensive and tends to weaken the sabot to such anextent'that there is a danger that it may break up before the projectilecompletes its travel through the bore of the gun thereby resulting inerratic and unpredictable trajectories and possible danger to personnelin the immediate vicinity of the gun. Furthermore, slighteccentrioities' f the sabot with respect to the projectile result instresses being set up in the sabot as it moves through the gun borethereby increasing the probability of premature breakup within the gun.

Some sabots are presently molded directly onto the projectile in aneffort to overcome the disadvantages of a machined sabot.. These sabotsburn away. as the proates Patenr.

that the rotating band of the projectile itself contacts the interior ofthe gun as it nears the muzzle. The sabot is generally enclosed in acombustible envelope in order to assure uniform initial burning of theprojectile. Not only must a gun having a special bore be used to firethe projectile, but the sabot must burn at a rapid and preciselycontrolled rate if the trajectory is to be accurate.

Accordingly, it is an object of this invention to provide a new andimproved sabot that is molded directly to the projectile for firingthrough a standard gun bore, which sabot is adapted to breakup in flightwithout undue distortion to the trajectory of the projectile.

Another object of this invention is to provide a new and improved moldedplastics sabot that is exactly concentric with respect to theprojectile. v

' Still another object is the provision of a projectile which includes arelatively thick basic sabot of high strength molded to a slug and arelatively thin plastics bourrelet --rotating bandobturator of suitableengraving properties molded to the basic sabot.

An additional object is the provision of a sabot composed of a filledthermosetting resin to withstand the pressures generated in a gun and athermoplastic resin shell on the sabot adapted to cooperate with the gunbarrel to provide a gas seal and to rotate the projectile as it movesthrough the gun bore.

A further object is the provision of a plastics sabot having a thineasily engraveable thermoplastic shell on its outer surface to reduceradial compressive loads on the sabot and prevent premature breakup ofthe sabot in the gun.

A still further object is the provision in a molded plastics sabothaving an aerodynamic break-out flange and a. preweakened portion in thesabot to assure controlled breakup thereof.

These and many other objects will become apparent When the followingspecification is considered in the light of the attendant drawingswherein like numerals designate like or similar parts throughout theviews and in which:

' Fig. 1 is an elevation partly in section of a compression mold showingthe plastic being molded about the prov jectile to form the basic sabot;

jectile moves through a bore of decreasing diameter so s Fig. 2 is anelevation partly in section showing a mold for forming the relativelyweak plastics shell about the basic sabot formed in the first step ofthe process;

Fig. 3 is a view of a finished sabot and projectile with various partsremoved to show the internal structure of the sabot particularly thefilled longitudinal slots; and

Fig. 4 is a section taken along the line 4-4 of Fig. 3 andviewed in thedirection of the arrows.

Referring now with greater particularity to the drawings'; the mold isformed of a support plate 10 carrying a body 11 encasing a hollow femalemold 13 disposed therein.

lower end, as viewed in the drawing, to receive the nose of an armourpiercing projectile or slug 16 and to position it accurately within themold. A plurality of inward- 1y extending vanes 17 are formed integralwith mold 13 to provide a series of longitudinal slots 12 in the basicsabot thereby providing a preweakened portion to assure proper breakupof the sabot as the projectile leaves the gun. A quantity ofthermosetting plastic is introduced into the mold above the slug 16 anda force or plunger 18 is driven downwardly through body 11 to urge theplastics material into the annular space between the slug 16 and theinterior of mold 13. In order to provide greater strength of the basicsabot, a quantity of glass The female portion 13 has an accuratelymachined, downwardly tapering insert 14 disposed at its of high strengthcould be used.

characteristics:

11,000 p.s.i.; compressive strength 4,900 p.s.i.; modulus of Thephysical characteristics of one such resin .(diallylphthalate) are asfollows: Specific, gravity 1.55; tensile strength 5000 p.s.i.;compressive strength 20,000 p.s.i.; modulus of elasticity 1.25 X psi.and percentage of elongation 1%.

Thermoplastics, on the other hand, soften when heat is applied andhardenupon cooling They. may be reworked'time afteritime. The thermoplasticused as the thin-walled shell is nylon which has the followingphysicalSpecific gravity 1.14; tensile strength elasticity 420,000 psi;percentage of elongation 60%.

Where a thermosetting resin is used as a mold or where a thermoplasticis molded onto a thermosetting resin there is substantially no adhesionbetween the twoplastics material material, however nylonthas been foundto be especially 7 encased in the outertliefnflo'plasticshell 31defining the bourrelet area 32 which rides in the grooves ofthe gunbarrel, the rotating band area 33 and the obturator 34 which provides agas seal as the projectile moves through i the gun barrel. i

This outer shell maybe composed of any thermoplastic suitable since itis slippery" and tends to lubricate the bore of the gun as itmovesthrough the bore. Furthermore, the nylon bourrelet-rotating band is easyon the gun bore and greatly extends the life of the gun. This a has beenestablished in tests of nylon rotating bands on "I'heinsert '14 containsan annular crown or ring 19 V which abuts the slug 16 when it is placedin the mold 13 so that a slight cusped relief portion 15 is formedbetween the forwardend of the sabot and the projectile. This reliefportion 15 forms the aerodynamic breakoutflange 21 is to; be understoodthat the mold as illustratedin Fig. l is shown only representatively,that is to say the force heating and mold heating apparatus is not shownand the ejection system is shown but schematically as an '20 mm.projectiles.

' form manner.

When i the projectile is ing the. trajectory of the armourpiercingprojectile 16 so that the projectile flies unerringly to the target.

The aerodynamic break out flange 21 serves to enhance breakupof thesabot as it moves through the air because this flange acts as a scoopramming air into the annular I cusp 15 formed between the sabot 27 andslug 16 thereby tending to ripthe" sabot frornthe slug in a radiallyuni- Although.this inventionhasbeen described with reference toone'e'mbodiment it should be apparentito those "skilled in the art afterreading'and understanding the specificatiorithat it is byno means solimited. ,Accordingly, the scope of this invention is to be limited onlyby the scope of the appended claims.

elongated receptacle 22 extending through a bore inplate 10 andreceiving the nose of the projectile which receptacle may bemovedupwardly by raising an externally operable knock out bar 24 after theplunger 18 has been withdrawn from the mold thereby to eject theprojectile containing the basic sabot 23.

The projectile, now secured to the basic sabot, is removed from the moldand any excess plastics material such as might be formed due toclearance between the force 18 and the female mold 13 is removed. Theprojectile containing sabot 23 is then placed in an injection mold ofthe type shown generally at 25. A quantity of thermoplastic material isinjected into the mold through channel 26 and flows into the annularspace between basic sabot 23 and the accurately machined mold insert 28.Mold 25 may be of any convenient design and, for the purposes ofillustration, isshown as. a-split mold opening along line a-a to permitremoval of the finished piece 27 from the mold. .Member 29' centers theprojectile and the basic sabot within the mold 28 to assure that thethin outer shell 31 will be disposed symmetrically with respect to theinner shell. The rotating band bourrelet--obturator combination is allformed simultaneously and integrally during this process and thepreweakcned longitudinal portions 12 .are filled with the thermoplasticmaterial. The, thermoplastic material is formed over the basic sabot butthere is substantially no adherence between them, the locking of theshell to the basic sabot being strictly mechanical thru the grooves inthe sabot and the thickened portions of the shell. After the thin outershell 31 is formed on the basic sabot 23, the entire unit is removedfrom the mold, the risers are machined off and the shell is ready to beattached to an appropriate cartridge case (not shown) in theconventionalmanner. A cartridge case retaining lip 35 and a crimping groove 36 areprovided for this purpose.

The ultimate configuration of: the shell is best appreciated byreferring to Figs: 3 and. 4 which more clearly sliow the projectile 16surrounded by the basic sabot 23 What is claimedas new and desired to besecured by Letters Patent of. the United States is:

1. An armour piercing projectile comprising; an armour piercing slug, athick-walledshock resistant plastics basic sabot formed of athermosetting resin molded to said slug a thin-walled easily engagedshell molded on said basic sabot and'providing; a rotating band assemblyfor the projectile, said shell being composed of a thermoplasticsmaterial and a breakout flange integral with the sabot to insureseparation of the sabot and slug during the early stages of the flightof the slug.

2. An armour piercing projectile comprising; an armour portions therein,a deformable thin-walled shell of thermoplastic material formed on theouter surface of said member to provide a readily engraveable rotatingband, obturator, and bourrelet at the outer surface thereof and a breakout flange formed as partof the member to insure separation of themember and slug during the early stages of the flight of the slug.

3. The projectile of claim 2 wherein the thin-walled shell is composedof nylon.

4. An armour piercing. projectile comprising; an armour piercing slug, asubstantially cylindrical thermosetting plastics member disposed about aportion of said slug in intimate contact therewith, said member having aplurality ofjgrooves formed therein to provide preweakened portions inthe member to promote breakup of said member during flight, a deformableshell of thermoplastic material formed on the outer surface of saidmember and filling said grooves thereby providing a readilyengraveablerotating band assembly at the outer surface of the member anda mechanical coupling with said member to insure rotation of thecylindrical plastics member with the deformable shell, and a break outflange integral with the member to insure separation of the member andslug during the early stages of the flight of the slug.

5. The projectile of claim t wherein the thermosetting' plastics memberis composed essentially of a glas fiber fired the sabot forms a gasseal, against thebore of the gun, guides and rotates the projectilcproperly through the bore of the gun and breaks up immediately upon exitfrom the gun without disturb,

reinforced plastics material and the shell is composed of nylon.

6. An armour piercing projectile comprising; an armour piercing slug, aglass fi ber reinforced thermosetting plastics member molded about saidslug, said member adapted to break up during flight of the projectilewithout substantially alfecting the trajectory thereof, a plurality ofgrooves formed in said member, an aerodynamic breakout flange formedintegral with the foreward end of said member and together with theforeward portion of the slug defining an annular recess formed betweenthe slug and the member, said breakout flange adapted to direct air intothe annular recess during flight of the projectile. To promote uniformbreakup of the member, a thermoplastics shell formed on the outersurface of said member and filling said grooves to provide a readilyengraveable rotating band assembly and a mechanical connection to insurerotation of the plastics member and its molded slug.

7. An armour piercing projectile comprising an armour piercing slughaving a body portion and a nose portion, a thick-walled thermosettingplastics basic sabot molded to said slug, a thin-walled comparativelyeasily engraved thermoplastics shell disposed about said basic sabot andproviding a rotating band assembly for the projectile, means integralwith said thin-walled shell engaging said thick-Walled sabot to insurerotation of said sabot with said shell and an annular breakout flange,said flange being integral with the sabot and encircling said slug inspaced relation to the nose portion of said slug.

8. An armour piercing projectile comprising an armour piercing slughaving a body portion and a nose portion, a substantially cylindricalthick-walled thermosetting plastics sabot disposed about said slug inintimate contact therewith, said member having a plurality oflongitudinal grooves formed therein, a comparatively easily deformablethin-walled shell of thermoplastic material formed on the outer surfaceof said sabot and providing a rotating band assembly for the projectile,said thermoplastic material entering and filling the grooves of thesabot, but not adhering thereto, to insure simultaneous turning of theshell and sabot with its attached slug through mechanical contact, andan annular breakout flange integral with the sabot and formed in spacedrelation encircling the nose portion of the armour piercing slug. I

9. An armour piercing projectile according to claim 8 wherein the thinwall thermoplastics shell is composed of nylon.

10.'An armour piercing projectile according to claim 8 wherein the sabotis essentially of a glass fibre reinforced diallylphthalate and theshell is composed of nylon.

11. A method of forming a two-piece plastics sabot for a projectilecomprising centering a slug in a compression mold, packing athermosetting resin about said slug, hardening to form a basic sabotattached to said slug, removing the slug and its attached basic sabot,centering said sabot and slug in an injection mold, and injecting athermoplastic resin to form a shell about said basic sabot.

Great Britain Mar. 25, 1946

